By regulating the flow of fluid through heat exchangers of an HVAC system, it is possible to adjust the amount of energy exchanged by the heat exchangers, for example to adjust the amount of energy that is delivered per time by a heat exchanger to heat or cool a room in a building or the amount of energy that is drawn by a chiller per time for cooling purposes. While the fluid transport through the fluid circuit of the HVAC system is driven by one or more pumps, the flow is typically regulated by varying the opening or position of valves, for example manually or by way of actuators. It is known that the efficiency of heat exchangers is reduced at high flow rates where the fluid rushes at an increased rate through the heat exchangers, without resulting in a significant increase in energy exchange.
State-of-the-art HVAC systems may include a variety of sensors, such as temperature sensors, flow sensors, and/or pressure sensors. Fluid flow in the HVAC system is controlled in dependence of sensor signals according to a variety of criteria and control algorithms.
With the number of sensors or sensor systems that are involved in the control of an HVAC system, as well as the complexity of the sensors or sensor systems, the risk of permanent or temporary sensor faults increases accordingly.
EP 2 339 256 discloses a method for controlling an air conditioner that comprises a plurality of indoor units. According to EP 2 339 256, the method calculates a replacement sensor value for an indoor unit, in case of a breakdown of a temperature sensor of any of the indoor units and controls the indoor unit based on the calculated value of the sensor. Specifically, the method of EP 2 339 256 calculates the sensor value for a temperature sensor of the inlet pipe to the respective indoor unit based on a temperature value measured by a temperature sensor of the outlet pipe from that indoor unit.
U.S. Pat. No. 5,630,325 discloses a controller for a heat pump system that includes a refrigerant compressor and an electrically controlled expansion valve. The controller compares the temperature of the refrigerant discharged from the compressor to predetermined extreme values, indicative of an alert condition. If the discharge temperature is above the predetermined extreme temperature, the discharge temperature is used to control the setting of the expansion valve; otherwise, the expansion valve is set to a predetermined setting.